Derived instances of Show have the following properties, which
are compatible with derived instances of Read:

The result of show is a syntactically correct Haskell
expression containing only constants, given the fixity
declarations in force at the point where the type is declared.
It contains only the constructor names defined in the data type,
parentheses, and spaces. When labelled constructor fields are
used, braces, commas, field names, and equal signs are also used.

If the constructor is defined to be an infix operator, then
showsPrec will produce infix applications of the constructor.

the representation will be enclosed in parentheses if the
precedence of the top-level constructor in x is less than d
(associativity is ignored). Thus, if d is 0 then the result
is never surrounded in parentheses; if d is 11 it is always
surrounded in parentheses, unless it is an atomic expression.

If the constructor is defined using record syntax, then show
will produce the record-syntax form, with the fields given in the
same order as the original declaration.

The method showList is provided to allow the programmer to
give a specialised way of showing lists of values.
For example, this is used by the predefined Show instance of
the Char type, where values of type String should be shown
in double quotes, rather than between square brackets.